Requirements for a Zero-Configuration IPv6 CPESanta Barbara93117CaliforniaUSAFredBaker.IETF@gmail.comOperations and Management
IPv6 OperationsThis note is a breif exploration of what is required for a CPE to be
auto-configurable from the perspective on an ISP or other upstream
network. It assumes that the CPE may also be IPv4-capable (probably
using NAPT), but that the requirements for that are well understood and
need no further specification. We observe that, in today's offerings, "IPv6-capable" has many
different meanings. These often require specific configuration and are
non-interoperable.The objective is to enable a customer to purchase a CPE router from a
mass market store, or for an ISP to purchase CPE Routers for its managed
service offering, that implement IPv6 and
can be attached to any residential/SOHO network and any ISP or other
upstream network "as is out of the box", and work correctly.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .The goal stated in requires that
downstream, which is to say within the home or SOHO , the CPE must
presume that there may exist systems that will autoconfigure themselves using information in a
Router Advertisement, and that there may
exist systems that require address assignment using DHCPv6. It may offer a DNS service using a
provider such as OpenDNS, Google Public DNS, Amazon Route 53, or some
other such service, or relay the address of an ISP-provided DNS
server.Similarly, the stated goal requires that upstream, the CPE must
presume that it will be required to solicit and observe a Router Advertisement, and learn an upstream DHCPv6 server address,either autoconfigure its upstream
address or derive one using DHCPv6,potentially learn an DNS server address from an RDNSS or from DHCPv6,and allocate IPv6 /64 prefixes for each of its interior subnets
using the IPv6 Prefix Options for
DHCP.Given that, it is in a position to offer IPv6 services in the
residential/SOHO network depending on the upstream IPv6
capabilities.As a result, a CPE needs to perform several steps, and come out of
the box configured to do so. These include: Upon detecting the upstream interface as "up", emit a Router Solicitation on it.If it receives a Router
Advertisement, verify its contents. These may include: If the RA contains a valid Prefix Information Option whose
prefix is available for autoconfiguration, create an address in
that prefix for that interface as specified in SLAAC.Failing that, use DHCPv6 to
request an address from the upstream network.In that same DHCP request, it MAY request an IA_PD delegation of a set of prefixes as
described in .If it has not already done so, the router should request an IA_PD delegation of a set of prefixes as
described in .Given an upstream interface and a delegation of prefixes to use
downstream, it should subdelegate a /64 prefix to each downstream interfaceallocate an address to each downstream interface using the
relevant prefixesstart announcing a periodic RA on each downstream interface.
This RA should include, in addition to usual information
elements, the RDNSS.When the CPE requests a set of prefixes from its upstream network,
there are several conditions that may apply: and presume a
/64 prefix on each IPv6 subnet.Each LAN to which the CPE connects may be presumed to require a
subnet - if not immediately, at some point in the future.There may be LANs in the residential/SOHO network that are not
attached to the CPE, but require subdelegation within the network
using DHCPv6 or HNCP.The IA_PD requests a prefix, and indicates its preference for a
"Length for this prefix in bits". By nature, this is exponential: if a
home requires 17 subnets, it will require the prefix to be no longer
than 59 bits, and therefore technically requesting at least 32 /64
prefixes. In fact, some ISPs have stated privately that they actually
allocate prefix lengths of 56, 60, or 64 (and therefore sets of 256, 16,
or 1 /64) depending on the CPE's request.The CPE should request as many as it thinks it might need, including
interior sub-delegation if it has an idea of what that may require.This memo asks the IANA for no new parameters.This note describes the use of existing features, each of which has
its own Security Considerations, and as such adds no new security
vulnerabilities.This memo calls for no personally identifiable information. The data
conveyed may, however, be correlatable with other data that is
personally identifiable. Such things are beyond the scope of this
document.Technologies described in this memo are not necessarily associated
with a human being, and as such violate no human rights.Jun 13 2017